We intend to examine with the electron microscope the microvasculature within myocardial tissue obtained from a series of diabetic patients electing corrective surgery for cardiac disabilities. In particular, we will evaluate the myocardial capillary and its basal lamina, in order to determine if the characteristic microangiopathy associated with the diabetic condition, which has been described in other tissues, can also be observed in the human diabetic heart. In addition, diabetes mellitus will be induced by pharmacologic means in the rat. Following onset of the disease, myocardial tissue will be examined electron microscopically on a sequential basis, for the purpose of studying the development of potential myocardial alterations, including capillary abnormalities, in the experimentally induced diabetic heart. The findings will then be compared and related to the information obtained from human diabetic hearts.